LM359 datasheet(8/24 Pages) NSC

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Application Hints (Continued)

The following figures illustrate typical biasing schemes for

AC amplifiers using the LM359:

The nV

BE biasing configuration is most useful for low noise

applications where a reduced input impedance can be ac-

commodated (see typical applications section).

OPERATING CURRENT PROGRAMMABILITY (I

SET)

The input bias current, slew rate, gain bandwidth product,

output drive capability and total device power consumption

of both amplifiers can be simultaneously controlled and opti-

mized via the two programming pins I

SET(OUT) and ISET(IN).

SET(OUT)

The output set current (I

SET(OUT)) is equal to the amount of

current sourced from pin 1 and establishes the class A bias-

ing current for the Darlington emitter follower output stage.

Using a single resistor from pin 1 to ground, as shown in

Fig-

ure 6, this current is equal to:

The output set current can be adjusted to optimize the

amount of current the output of the amplifier can sink to drive

load capacitance and for loads connected to V

+. The maxi-

mum output sinking current is approximately 10 times

ISET(OUT) . This set current is best used to reduce the total

device supply current if the amplifiers are not required to

drive small load impedances.

SET(IN)

The input set current I

SET(IN) is equal to the current flowing

into pin 8. A resistor from pin 8 to V

+ sets this current to be:

SET(IN) is most significant in controlling the AC characteris-

tics of the LM359 as it directly sets the total input stage cur-

rent of the amplifiers which determines the maximum slew

rate, the frequency of the open loop dominant pole, the input

resistance of the (−) input and the biasing current I

b(−). All of

DS007788-8

FIGURE 3. Biasing an Inverting AC Amplifier

DS007788-9

FIGURE 4. Biasing a Non-Inverting AC Amplifier

DS007788-10

FIGURE 5. nV

BE Biasing

DS007788-11

FIGURE 6. Establishing the Output Set Current

DS007788-12

FIGURE 7. Establishing the Input Set Current

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